#ifndef LOCALONLY
#include "race.h"
#endif // LOCALONLY
#include <bits/stdc++.h>
using namespace std;
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i++)
#define FORD(i, b, a) for (int i = (b), _a = (a); i >= _a; i--)
#define REP(i, n) for (int i = 0, _n = (n); i < _n; i++)
#define BIT(i, x) (((x) >> (i)) & 1)
#define MK(i) (1LL << (i))
#define all(v) v.begin(), v.end()
#define sz(v) ((int)v.size())
#define F first
#define S second
template <class t> bool maxi(t &x, t const &y)
{
return x < y ? x = y, 1 : 0;
}
template <class t> bool mini(t &x, t const &y)
{
return x > y ? x = y, 1 : 0;
}
int const N = 2e5 + 5;
int n, k;
vector<pair<int, int>> adj[N];
map<long long, int> mp[N];
int h[N];
long long d[N];
int res = N;
void DFSPrepare(int u, int p)
{
for (auto &e : adj[u])
{
int v = e.F;
int w = e.S;
if (v == p) continue;
d[v] = d[u] + w;
h[v] = h[u] + 1;
DFSPrepare(v, u);
}
}
void DFS(int u, int p)
{
mp[u][d[u]] = h[u];
for (auto &e : adj[u])
{
int v = e.F;
if (v == p) continue;
DFS(v, u);
if (sz(mp[u]) < sz(mp[v])) swap(mp[u], mp[v]);
for (auto &p : mp[v])
{
auto it = mp[u].find(k + 2 * d[u] - p.F);
if (it != mp[u].end()) mini(res, it->S + p.S - 2 * h[u]);
}
for (auto &p : mp[v])
{
int &x = mp[u][p.F];
if (x == 0) x = p.S;
else mini(x, p.S);
}
}
}
int best_path(int nn, int kk, int hh[][2], int ll[])
{
n = nn, k = kk;
REP(i, n - 1)
{
int u = hh[i][0] + 1;
int v = hh[i][1] + 1;
int w = ll[i];
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
DFSPrepare(1, -1);
DFS(1, -1);
return res == N ? -1 : res;
}
#ifdef LOCALONLY
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int n, k;
int h[6767][2];
int l[6767];
cin >> n >> k;
REP(i, n - 1) cin >> h[i][0] >> h[i][1] >> l[i];
cout << best_path(n, k, h, l);
return 0;
}
#endif //LOCALONLY
